Wednesday marked another rough day in travel in the U.S. as hundreds of flights were again canceled across the country.

According to FlightAware, U.S. airlines had canceled more than 800 flights by 12:30 p.m. ET on Wednesday afternoon. That comes a day after nearly 1,300 flights were canceled across the country on Tuesday.

United alone canceled 158 fights Wednesday, representing about 7% of the day's air traffic. Delta also canceled 103 flights.

The travel woes continue a trend that started last week following the Christmas holiday. Several airlines have confirmed that staffing shortages caused by COVID-19 infections have led to flights being canceled in the past week.

CNN obtained an internal memo from United last Thursday that noted that the rise of the more contagious omicron variant had a "direct impact on our flight crews and the people who run our operation."

In a statement earlier this week, Delta Airlines told NPR that omicron staffing shortages also factored into its decision to cancel 344 flights on Christmas Day. NBC News reports that JetBlue and Alaska Airlines have also cited staffing shortages and COVID-19 outbreaks as reasons for canceling flights.

The flight cancelations will likely continue later on in the week. FlightAware says about 400 domestic flights scheduled for Thursday have already been canceled, in addition to 67 flights already canceled for Friday.